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"We're now seeing them come into residential premises as well. It's nothing to do with hygiene."

The blood-sucking insects are often brought to New Zealand in luggage carried by visitors from Europe, Asia and New York, where they have developed resistance to the pyrethroid products used to exterminate them.

They usually climb from cracks in walls or bed-bases about 2am or 3am to feed on their sleeping host.

"You wake up in the morning and you don't even know you've been bitten until a bite comes up," said Mr McDonald, who reported the 250 per cent increase in calls. "It looks similar to a mosquito bite."

Owen Stobart, of Aces Pest Control Auckland, said he used to get about one call a month for bedbugs, now it was more like one a week.

"They're actually the insect most resistant to chemicals in the world because they have a coating wax over their body," he said. "It's like applying a chemical to someone with a raincoat on - you just can't get to them. They're also very good at hiding, they like to squeeze into small gaps. They are hands-down the worst infestation to have."

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If they had warmth and a host, he said, bedbugs would keep multiplying "exponentially" and wouldn't go away. "They can produce 40 young every six weeks - little pin-head-sized opaque babies. Once they get going they really get going."

Entomologist Ruud "the Bugman" Kleinpaste said bedbugs were prolific because the world was "overrun" by their prey - humans.

The amount of pesticide used to fight bedbugs was making them resistant.

Q&A BedbugsWhat do bedbugs look like?Oval-shaped, flat, reddish-brown and up to 5mm long. Immature bed bugs may be pale, almost translucent

Can their bites be harmful?Some people have no reaction and don't develop bite marks, but most get a series of itchy bites. Some people are allergic to bedbug saliva and can get painful swelling. In very rare cases people can have a severe allergic reaction

How do you prevent bedbugs?Check second-hand furniture before bringing it into your home, avoid buying second-hand mattresses

And if you've been travelling?Check hotel rooms before settling in and keep your bags off the floor. When you get home, wash clothes in the hottest water the fabric can tolerate and vacuum your bags, paying special attention to creases.DermNet NZ/Ministry of Health